1. Field of the Invention
This invention relates to the general field of measurement and testing of wound roll structures. Roll structures are formed from "webs"-which may be any windable material, such as paper, plastic, film, fabric, coated laminates, composites, metal foil and the like. More specifically, this relates to measuring wave parameters within a roll and then analyzing the results to determine a radial pressure versus the roll radius.
2. Description of the Related Art
Most roll structure measurement is presently done with destructive and intrusive measuring devices. These are generally limited to research and development applications. The roll structure measurement techniques are usually qualitative and not quantitative. Examples include the Rhometer, Schmidt Hammer or even a calibrated thumb. Most quantitative techniques are intrusive and destructive, such as Force Sensitive Resistors (see Good, J. K. et al., "Predicting Internal Stresses in Center-Wound Rolls With An Undriven NIP Roller," and U.S. Pat. No. 4,594,880) and pull tabs. Other quantitative techniques, such as the density analyzer, require the rolls to be wound on special winders, with high precision measurement equipment attached. Some techniques only measure surface parameters (U.S. Pat. Nos. 3,425,267; 3,540,270).
Since many, if not most, web materials are stored and/or processed in a wound form, there is a need for a method and device to measure the internal parameters of the wound roll at any point or time in its formation, transport, storage or usage. As noted above, most methods to date are either destructive and invasive, or they only measure the surface parameters, or they are only measurable at the time of roll formation.